Misconceptions about the chemistry of aqueous chlorine atoms and HClOH˙(aq), and a revised mechanism for the photochemical peroxydisulfate/chloride reaction

Abstract

It is widely considered that aqueous chlorine atoms (Cl˙) convert to the species HClOH˙ with a half life of about 3 μs and that this species plays an important role in the chemistry of aqueous chlorine atoms. Here it is shown that there is no firm evidence for the existence of HClOH˙ as a species distinct from Cl˙, that the chemistry attributed to HClOH˙ can be accounted for by other well-established species, and that almost all published mechanisms that include reactions of HClOH˙ violate the principle of detailed balancing. More than 100 publications are identified that violate the principle of detailed balancing with HClOH˙ reactions. Proposals for the participation of HClOH˙ in reaction mechanisms originated in studies of the photochemical peroxydisulfate/chloride reaction; here we provide a revised mechanism that omits HClOH˙, complies with the principle of detailed balancing, and has a minimal number of reaction steps.